This invention relates to a keyboard apparatus for an electronic musical instrument such as an electronic piano.
As shown in FIG. 6, there is conventionally known a keyboard apparatus for an electronic musical instrument, comprising a key "a" which is provided so as to be rotatable about a fulcrum b and a hammer d which is supported on this key "a" so as to be rotatable about a fulcrum c. This hammer d is provided for the purpose of obtaining such a feeling of touching the key as in an acoustic piano. It has a predetermined weight and its center of gravity lies in the right-hand side in the figure.
When the key "a" is depressed, the hammer d rotates via a supporting member e. When the key "a" is released from depression, the hammer d and the key "a" are returned to their original positions by the weight of the hammer d.
In the above-mentioned conventional apparatus, it is possible to obtain the feeling of touching the key as in the acoustic piano only when the key is depressed with a force which is stronger than a predetermined one. When the key is depressed very gently or weakly, as shown in FIG. 7, a load greater than before begins to be applied from the point O and its value reaches a maximum at point P. It is impossible to obtain the feeling of touching the key as in the acoustic piano in which, when the key is further depressed, the load is released at a stretch (by means of a mechanism called a let-off mechanism).